The present invention relates to a rubber composition containing a dinitrodiamine compound for improving dynamic properties of the vulcanized rubber containing filler.
Recently, there have been caused urgent social requirements for improving rubber tires with regard to rate of fuel consumption of passenger cars and for extending running life of large size tires in motor trucks and buses. Thus, the improvement in dynamic properties such as resilience and exothermic properties of vulcanized rubber used widely for tires and other rubber products has become important to meet the requirements.
As methods for improving the dynamic properties, such methods as improvements in, for example, microstructure or molecular weight distribution of rubber, improvements in compounding manner of rubber chemicals or fillers, addition of dynamic property improvers and the like are well known in the art.
Among these methods, the method of adding dynamic property improvers has been paid attention since the method can improve the dynamic properties more easily in comparison with the other methods and can be applied also to natural rubber for the improvement. There have been developed as the dynamic property improvers, for example, 8-oxyquinoline derivatives having a specific structure as disclosed in Unexamined Published Japanese Patent Application No. 118837/83 and nitro compounds containing sulfur atoms disclosed in Unexamined Published Japanese Patent Application No. 18740/84.
However, both the 8-oxyquinoline derivatives and the sulfur-containing nitro compounds were, in spite of their excellent effects on improvements in resilience and exothermic property, not entirely satisfactory due to their undesirable effects of accelerating the scorching property remarkably or deteriorating the flex-cracking resistance.
On the other hand, dinitrodiamines are known to be useful as a metal additive, an additive for oils or an intermediate thereof, which include, for example, N,N'-bis(2-methyl-2-nitropropyl)piperazine [J. Am. Chem. Soc., 78, 482 (1956)]; N,N'-bis[(1-nitrocyclohexyl)-methyl]-1,2-diaminoethane and N,N'-bis[(1-nitrocyclohexyl)methyl]-1,6-diaminohexane [J. Org. Chem., 23, 1115 (1958)]; N,N'-bis(2-methyl-2-nitroethyl)-1,2-diaminoethane [Aust. J. Chem., 21, 2797 (1968)] and the like. They are also known to be used, for example, as a metal chelating agent to be added after reducing nitro groups into amino groups. However, nothing has been reported about these dinitrodiamines that they are useful as additives for improving the dynamic properties such as resilience and exothermic property of vulcanized rubber.
As methods for producing these dinitrodiamines, there are disclosed respectively in J. Am. Chem. Soc., 78, 482 (1956) a method for producing N,N'-bis(2-methyl -2-nitropropyl)piperazine by reacting piperazine, 2-nitropropane and formaldehyde at temperatures up to a steam bath temperature, and in J. Org. Chem., 23, 1115 (1958) a method for producing N,N'-bis[(1-nitrocyclohexyl)methyl]-1,2-diaminoethane by reacting 1,2-diaminoethane, nitrocyclohexane and formaldehyde at a temperature of 60.degree. C. or below.
The former method uses, in principle, a secondary diamine as a raw material, but when a primary diamine is used as the raw material to carry out in accordance with the method, yield of the aimed dinitrodiamine compound is appreciably decreased due to formation of a variety of by-products.
The latter method is a reaction at a low temperature in which formaldehyde is used in an excessive amount than the amounts of the primary diamine and the nitroalkane, however, it produces thermally unstable by-products such as trinitrodiamines, tetranitrodiamines or the like and various kinds of by-products having unidentified structure. Accordingly, the method is not entirely satisfactory because of the low yield of the aimed dinitrodiamine compound.